1. Field of the Invention
The present invention relates to an electrical stimulator.
2. Description of the Related Art
A biomedical signal such as a series of pulses is used to detect periods during which it is preferred to stimulate a living body. Electrical stimulation is then applied to the living body mainly during these periods. This method is very effective in improving blood circulation and is not comparable with a conventional electrical stimulator, for example, a low-frequency treatment apparatus.
What are referred to as "periods during which it is preferred to apply stimulation to a living body" are periods (diastolic periods) in the activity of the heart during which blood returns to the heart via the veins. In general, the veins have no source of a force for driving blood. If a supplementary power for driving blood is applied to the veins, the blood circulation is immediately improved.
To be more specific, a biomedical signal such as an electrocardiogram is used to detect diastolic periods. Stimulation is then applied mainly during the diastolic periods. This modality accelerates blood circulation very efficiently, which is not comparable with a conventional electrical massager, low-frequency treatment device, or other electrical stimulator. Moreover, acceleration of blood circulation results in weight reduction.
When an attempt is made to constitute the foregoing apparatus, the apparatus comprises, for example, a means for detecting a heart-beat signal, a means for discriminating a diastolic signal from the heart-beat wave, and an output means for outputting electrical stimulation pulses in response to the input of the diastolic signal.
In the output means for outputting electrical stimulation pulses in response to the input of a diastolic signal, when the means is materialized in practice, some problems arise. That is to say, an initial transient delay due to component parts occurs before the output of electric stimulation pulses. When a microcomputer is employed, a program routine for preventing an erroneous operation caused by noises is installed. Consequently, the output of electrical stimulation pulses is not completely locked onto a diastolic signal. For constituting a portable apparatus, the number of parts must be minimized. Any other device can therefore not be incorporated.
In the aforesaid apparatus, it is very important to detect diastolic periods.
In a method offering a means for detecting diastolic period, systolic periods are detected first, and then reversed or removed. A systolic period refers, for example, as indicated with SS in FIG. 1, to a period from the a minimum value to a peak value. The lowest value indicating the start of a systolic period is not detected accurately in practice or hardly detected due to artifacts or depending on a region in which a biomedical signal is detected.
Unlike a pulse monitor, the apparatus must detect not only pulses but also output and stop electrical stimulation pulses. Moreover, a means that can be operated more easily and reliably is required to detect systolic periods or diastolic periods.
On the other hand, a pulse wave varies depending on the activity of the heart. Violent exercises or psychological excitation results in smaller pulse durations and narrower diastolic periods.
In this state, even if electrical stimulation is applied during diastolic periods, only a limited effect is expected. Moreover, electrical stimulation may not be locked onto the diastolic periods. On the contrary, electrical stimulation may be applied during (systolic) periods during which the heart feeds blood, which degrades the force of feeding blood. An extra load is imposed on the heart. In this kind of electrical stimulator, which is preferred to be used for a prolonged period of time continuously, a means for copying with narrowing pulse durations of a pulse wave has been in need.